Nlos wireless backhaul downlink communication

ABSTRACT

A method for communicating over a wireless backhaul channel comprising generating a radio frame comprising a plurality of time slots, wherein each time slot comprises a plurality of symbols in time and a plurality of sub-carriers in a system bandwidth, broadcasting a broadcast channel signal comprising a transmission schedule to a plurality of remote units in a number of consecutive sub-carriers centered about a direct current (DC) sub-carrier in at least one of the time slots in the radio frame regardless of the system bandwidth, and transmitting a downlink (DL) control channel signal and a DL data channel signal to a first of the remote units, wherein the DL data channel signal is transmitted by employing a single carrier block transmission scheme comprising a Discrete Fourier Transform (DFT) spreading for frequency diversity.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Application No. 17/135,393filed Dec. 28, 2020, which is a continuation of U.S. Application No.16/408,590 filed May 10, 2019, which is a continuation of U.S.Application No. 14/297,145 filed Jun. 5, 2014, which claims the benefitof U.S. Provisional Pat. Application 61/831,214, filed Jun. 5, 2013 byJune Chul Roh, et. al., and entitled “DATA TRANSMISSION AIR-INTERFACEFOR NLOS WIRELESS BACKHAUL SYSTEMS”, U.S. Provisional Pat. Application61/831,217, filed Jun. 5, 2013 by June Chul Roh, et. al., and entitled“DOWNLINK OF NLOS WIRELESS BACKHAUL SYSTEMS”, and U.S. Provisional Pat.Application 61/831,229, filed Jun. 5, 2013 by June Chul Roh, et. al.,and entitled “UPLINK OF NLOS WIRELESS BACKHAUL SYSTEMS”, all which areincorporated herein by reference in their entirety.

BACKGROUND

A radio access network (RAN) refers to a network between mobile devices(e.g. mobile phones, personal digital assistants (PDAs), laptops, or anyuser equipment) and a core network. For example, an area may be dividedgeographically into a plurality of cells and/or cell sectors, where eachcell and/or cell sector may be served by a wireless base stationcommunicating to the core network. Wireless backhaul may refer to thepart of the RAN from the wireless base station to the core network. Somewireless backhaul links may be configured for point-to-point (P2P)line-of-sight (LOS) channels (e.g. at about six to about forty-twogigahertz (GHz) microwave frequency band). Thus, such wireless backhaullinks may employ single carrier waveforms for transmission andtime-domain equalization (TDE) techniques at the receivers. However, inorder to meet the growing demand for voice and/or data services overRAN, cell density may be increased, for example, by adding small cellsin the neighborhood of macro cells. As such, the density of theassociated backhaul links may increase and the P2P LOS wireless backhaulcommunication mechanisms may not be suitable.

SUMMARY

A non-line-of-sight (NLOS) wireless backhaul downlink communication isdisclosed herein. In one embodiment, a method for communicating over awireless backhaul channel includes generating a radio frame comprising aplurality of time slots, wherein each time slot comprises a plurality ofsymbols in time and a plurality of sub-carriers in a system bandwidth.The radio frame comprises an adjustable link directionality ratio of anumber of the time slots for an uplink (UL) direction and the number oftime slots for a downlink (DL) direction to provide traffic loadbalancing. The method further includes broadcasting a broadcast channelsignal to a plurality of remote units in a number of consecutivesub-carriers centered about a direct current (DC) sub-carrier in atleast one of the time slots in the radio frame regardless of the systembandwidth. The broadcast channel signal comprises a transmissionschedule comprising slot assignments that indicate a link direction anda transmission opportunity for a first of the plurality of remote units.The method further includes transmitting a DL control channel signal anda DL data channel signal to the first remote unit, wherein the DLcontrol channel signal comprises DL control information that controlstransmission of the DL data channel signal. The broadcast channelsignal, the DL control channel signal, and the DL data channel signalare transmitted by employing a time-frequency multiplex scheme. The DLdata channel signal is transmitted by employing a single carrier blocktransmission scheme comprising a Discrete Fourier Transform (DFT)spreading for frequency diversity.

In another embodiment, an apparatus includes a processing resource and aradio front end interface. The processing resource is configured toperform single carrier modulation on a plurality of data bit streams togenerate a plurality of Single Carrier-Frequency Division MultipleAccess (SC-FDMA) frames. To perform the single carrier modulation oneach data bit stream, the processing resource is further configured toperform symbol mapping on each data bit stream to generate a pluralityof modulated data symbols and to perform DFT precoding on the modulateddata symbols. The processing resource is further configured to performfrequency-time multiplexing to combine at least one of the SC-FDMAframes with an Orthogonal Frequency Division Multiplexing (OFDM) frameto generate a digital radio frame. The radio front end interface iscoupled to the processing resource and configured to cause the digitalradio frame to be transmitted to a wireless backhaul remote unit.

In yet another embodiment, a wireless backhaul communication systemincludes a transmitter comprising a Reed Solomon (RS) encoder configuredto perform RS encoding on a DL data bit stream to generate a pluralityof RS codewords, a byte interleaver coupled to the RS encoder andconfigured to perform byte interleaving across the plurality of RScodewords, and a Turbo encoder coupled to the byte interleaver andconfigured to perfrom Turbo encoding on the interleaved RS codewords togenerate one or more Turbo codewords. Each Turbo codeword is encodedfrom multiple RS codewords. The transmitter further includes a symbolmapper coupled to the Turbo encoder and configured to modulate and DFTprecode the Turbo codewords, a transmission control frame, and abroadcast frame separately. The broadcast frame comprises a transmissionschedule for a plurality of wireless backhaul remote units. Thetransmitter further includes a sub-carrier mapper coupled to the symbolmapper and configured to generate a digital radio frame comprising aplurality of symbols in time and a plurality of sub-carriers in a systembandwidth. To generate the digital radio frame, the sub-carrier mapperis to further configure to map the DFT precoded broadcast frame onto afirst set of the sub-carriers centered about a DC sub-carrier. The firstset of sub-carriers comprises a fixed number of consecutive sub-carriersregardless of the system bandwidth. The sub-carrier mapper is furtherconfigured to map the DFT precoded transmission control frame onto asecond set of the sub-carriers near a lower frequency edge and near ahigher frequency edge of the system bandwidth and map the DFT precodedTurbo codewords onto frequency sub-carriers different than the first setof sub-carriers and the second set of sub-carriers. The wirelessbackhaul communication system further includes a radio front endcomprising an antenna and coupled to the transmitter. The radio frontend is configured to convert the digital radio frame to an analog signaland transmit the analog signal via the antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of exemplary embodiments of the invention,reference will now be made to the accompanying drawings in which:

FIG. 1 shows a block diagram of a point-to-multi-point (P2MP) backhaulsystem in accordance with various embodiments;

FIG. 2 shows a block diagram of a wireless backhaul device in accordancewith various embodiments;

FIG. 3 shows a block diagram of a transmitter for single antennatransmission in accordance with various embodiments;

FIG. 4 shows a block diagram of a transmitter for rank-1 transmission inaccordance with various embodiments;

FIG. 5 shows a block diagram of a transmitter for rank-2 transmission inaccordance with various embodiments;

FIG. 6 shows a block diagram of a transmitter for DL non-data channeltransmission in accordance with various embodiments;

FIG. 7 shows a block diagram of another transmitter for DL non-datachannel transmission in accordance with various embodiments;

FIG. 8 shows a block diagram of a transmitter that combines SC-FDMA andOFDM transmissions in accordance with various embodiments;

FIG. 9 shows a block diagram of a wireless backhaul radio frame inaccordance with various embodiments;

FIG. 10 shows a block diagram of a DL slot in accordance with variousembodiments;

FIG. 11 shows a block diagram of another DL slot in accordance withvarious embodiments;

FIG. 12 shows a block diagram of a special slot in accordance withvarious embodiments;

FIG. 13 shows a block diagram of another special slot in accordance withvarious embodiments;

FIGS. 14A and 14B show a block diagram of a UL slot in accordance withvarious embodiments;

FIGS. 15A/B shows a block diagram of a wireless backhaul radio sub-framein accordance with various embodiments;

FIG. 16 shows tables of uplink-downlink (UL-DL) slot configurations inaccordance with various embodiments;

FIG. 17 shows a table of UL-DL slot configurations and corresponding DLratios and UL ratios in accordance with various embodiments;

FIG. 18 shows a block diagram of a forward error correction (FEC)encoding method in accordance with various embodiments;

FIG. 19 shows a flowchart of a FEC encoding method in accordance withvarious embodiments; and

FIG. 20 shows a flowchart of an initial random access method inaccordance with various embodiments.

DETAILED DESCRIPTION

The following discussion is directed to various embodiments of theinvention. Although one or more of these embodiments may be preferred,the embodiments disclosed should not be interpreted, or otherwise used,as limiting the scope of the disclosure, including the claims. Inaddition, one skilled in the art will understand that the followingdescription has broad application, and the discussion of any embodimentis meant only to be exemplary of that embodiment, and not intended tointimate that the scope of the disclosure, including the claims, islimited to that embodiment.

In a RAN, mobile devices may connect to a core network via a pluralityof links. For example, a first link (e.g. a mobile access channel, suchas a Long Term Evolution (LTE) communication channel) may be between themobile devices and a wireless base station serving a cell that coversthe location of the mobile devices, a second link (e.g. a wirelessbackhaul channel) may be between the wireless base station (e.g.comprising a wireless backhaul remote unit (RU)) and a wireless backhaulhub (HU), and a third link may be between the wireless backhaul hub andthe core network. As the tendency in RAN topology is to increase celldensity by adding a plurality of small cells in the neighborhood ofmacro cells, the density of the associated backhaul links may increase.The densely populated small cell backhauls may lead to NLOS backhaulchannels. As such, the differences between mobile access channels andwireless backhaul channels may decrease as the backhaul link densityincreases. Thus, NLOS wireless backhaul communication may employ asubstantially similar point-to-multi-point (P2MP) topology andair-interface mechanisms as in the mobile access channels. However,wireless backhaul may require some different features from the mobileaccess. For example, wireless backhaul communication may comprisesparser spectrum availability, tighter latency (e.g. less than aboutfive milliseconds (ms) may be desirable), and steadier operations (e.g.no handover, lower disconnection rate, no mobility support, etc.). Inaddition, wireless backhaul may support operation at a bit error rate(BER) (e.g. around 10⁻ ¹⁰) substantially lower than mobile accesschannels.

Embodiments of the NLOS wireless backhaul communication disclosed hereininclude a wireless backhaul radio frame configuration and basebandgeneration schemes for small cell backhaul. The small cell backhaul mayemploy a P2MP configuration, for example, one HU communicating to aplurality of RUs located at mobile base stations, each serving a celland/or a cell sector. The wireless backhaul communication may employ atime division duplex (TDD) scheme for UL and DL transmissions, where asingle frequency band (e.g. 5, 10, and/or 20 megahertz (MHz)) may beshared between a UL channel and a DL channel by multiplexing the UL andDL transmissions in a time domain. A radio frame may comprise apredetermined number of sub-carriers (e.g. according to sub-carrierspacing and bandwidth) and may span a pre-determined time interval. Inan embodiment, a radio frame may comprise two sub-frames (e.g. halfframe), each sub-frame may comprise about ten time slots, and each slotmay comprise about seven SC-FDMA symbols in time. In a radio frame, oneor more time slots may be assigned to a RU for UL and/or DLtransmissions and may vary depending on traffic load. In order toprovide low transmission latency for wireless backhaul, a time slot maybe configured to be about 0.5 ms duration. In an embodiment, DLtransmission may comprise a plurality of physical layer (PHY) channels,such as a physical DL shared channel (PDSCH), a physical DL controlchannel (PDCCH), a physical hybrid automatic repeat request indicatorchannel (PHICH), and a physical broadcast channel (PBCH). ULtransmission may also comprise a plurality of PHY channels, such as aphysical UL shared channel (PUSCH), a physical UL control channel(PUCCH), and a physical random access channel (PRACH). A time slot maycarry one or more of the UL PHY channels or DL PHY channels byfrequency-time multiplexing. In addition, each radio frame may carry asynchronization sequence (SS) for frame detection and/or synchronizationand each time slot may comprise a pilot symbol (PS) for channelestimation and/or frequency and/or timing offset tracking. In anembodiment, a wireless backhaul system may employ SC-FDMA for both ULand/or DL transmissions, where SC-FDMA may provide a substantially lowerpeak-to-average-power ratio (PAPR) than OFDM. In addition, SC-FDMA maybe combined with Orthogonal Frequency Division Multiple Access (OFDMA)through sub-carrier mapping to provide frequency diversity and maintaina substantially low PAPR. The wireless backhaul system may employ ahigher-order modulation (e.g. 256 Quadrature Amplitude Modulation (QAM))to provide higher data rate and a FEC scheme that combines RS encodingas outer code, Turbo encoding as inner code, and a hybrid automaticrepeat request (HARQ) scheme to provide a low BER (e.g. about 10⁻¹⁰).

FIG. 1 shows a block diagram of a P2MP backhaul system 100 in accordancewith various embodiments. The system 100 may comprise a HU 110 and aplurality of RUs 120 (e.g. RU 1, RU 2, ..., RU K) configured in a P2MPconfiguration. The HU 110 may be communicatively coupled to the RUs 120via air-interface links 130. The links 130 may comprise wireless NLOSchannels. The links 130 may be bi-directional links comprising both ULand DL transmissions, where UL transmissions may refer to transmissionsfrom RUs 120 to HU 110 and DL transmissions may refer to transmissionsfrom HU 110 to RUs 120.

The HU 110 may be a wireless equipped device configured to communicatewith a plurality of RUs 120 over the air-interface links 130 forbackhaul connectivity and management. The HU 110 may comprise a wirelesstransceiver or a separate wireless transmitter and receiver with one ormore antennas. The HU 110 may be configured to transmit DL radio signalsto one or more RU 120s and receive UL radio signals from one or more RUs120 by employing a SC-FDMA scheme for transmissions in both UL and DL.The HU 110 may employ a TDD scheme for multiplexing UL and DLtransmissions in time and a time domain multiple access (TDMA) scheme toschedule transmission in units of time slots for the RUs 120. The HU 110may provide connectivity between the RUs 120 and a core network (e.g.via a physical link, such as an optic fiber link). The core network maybe a mobile operator’s network, a packet switched telephone network(PSTN), or a packet switched data network (PSDN). In some embodiments, aHU 110 may serve about four to about eight RUs 120.

The RUs 120 may be a wireless equipped device configured to communicatewith a HU 110 over the air-interface links 130. Each RU 120 may comprisea wireless transceiver or a separate wireless transmitter and receiverwith one or more antennas and may be configured to transmit UL radiosignals to the HU 110 and receive DL radio signals from the HU 110 byemploying a SC-FDMA scheme. In some embodiments, the RU 120 may belocated in a mobile base station that serves a geographically dividedarea (e.g. a small cell), where the mobile base station may communicatewith a plurality of mobile devices (e.g. mobile phones, laptops, or anymobile user equipment) situated in the served area. In some otherembodiments, the RU 120 may be attached or connected with a digital linkin a physical location (e.g. a lamp post).

In an embodiment, UL and/or DL transmissions between a HU 110 and RUs120 may be in terms of radio frames over links 130. A radio frame mayspan a predetermined system bandwidth, for example, five, ten, or twentyMHz, and a predetermined time interval. For example, a radio frame maycomprise a plurality of sub-carriers (e.g. with sub-carrier spacing ofabout fifteen kilohertz (kHz)) in the frequency domain and about twosub-frames in a time domain. Each sub-frame may comprise about ten timeslots and each slot may comprise about seven symbols. HU 110 may assignone or more time slots for a RU 120 in a radio frame and may adjust theswitching between UL and DL based on traffic load. HU 110 and RUs 120may communicate via several UL and DL channels, which may befrequency-time multiplexed in a radio frame and may operate in a TDDmode for DL and UL duplexing. For example, DL PHY channels may comprisea PDSCH for transporting DL data, a PDCCH for transporting physicallayer transmission controls, a PBCH for broadcasting system informationand/or transmission schedules, and/or a PHICH for transporting HARQfeedbacks for UL transmissions (e.g. reception statuses). UL PHYchannels may comprise a PUSCH for transporting UL data, a PUCCH fortransporting UL controls and reports (e.g. wide-band Channel QualityIndicator (CQI), Rank Indication (RI), HARQ feedbacks for DLtransmissions, etc.), and a PRACH for transporting random accesssequences for initial channel access. In addition, each radio frame maycarry a SS to allow frame detection and/or frame synchronization at a RU120 and each time slot may comprise a PS for channel estimation and/orfrequency and/or time offset tracking at a HU 110 and/or a RU 120.

FIG. 2 shows a block diagram of a wireless backhaul device 200 inaccordance with various embodiments. Device 200 may act as a HU (e.g. HU110) or a RU (e.g. RU 120) in a wireless backhaul system (e.g. system100). As shown in FIG. 2 , the device 200 may comprise digitalinterfaces 210, a processing unit 230, a data storage unit 240, and aradio frequency (RF) interface 220. The digital interfaces 210 may beconfigured to receive digital data streams from external devices and/ortransmit digital data streams to external devices. In some embodiments,digital interfaces 210 may include high speed serializer/de-serializer(SerDes) lanes, external memory interfaces (EMIFs), universal serial bus(USB) interfaces, serial peripheral interfaces (SPIs), universalasynchronous receive/transmit (UART) interfaces, Integrated-IntegratedCircuit interfaces (12Cs), general purpose digital Input/Outputs(GPIOs), etc.

A processing unit 230 may be coupled to the digital interface 210 toprocess the data streams received from the digital interface 210 orgenerate and transmit data streams to the digital interface 210. Theprocessing unit 230 may comprise one or more processors (e.g., single ormulti-core processors, a digital signal processor, etc.), one or morehardware accelerators, one or more computers, and/or data storage unit240, which may function as data stores, buffers, etc.

In some embodiments, the processing unit 230 may include a plurality ofhardware accelerators designed specifically for wireless backhaulcommunication. Some examples of hardware accelerators may include Turboencoding and/or decoding, Viterbi decoding, bit rate processing, FastFourier Transform (FFT), digital down and/or up conversions (DDUC),crest factor reduction (CFR), digital pre-distortion (DPD), packetprocessing, security processing, etc.

The processing unit 230 may comprise a wireless backhaul transceivermodule 231 stored in internal non-transitory memory in the processingunit 230 to permit the processing unit 230 to implement a basebandtransmit chain, such as transmitter 300, 400, 500, 600, and/or 700,methods 1600 and/or 1700, a baseband receiving chain, and/or any otherschemes as discussed herein. In an alternative embodiment, the wirelessbackhaul transceiver module 231 may be implemented as instructionsstored in the data storage unit 240, which may be executed by theprocessing unit 230.

The data storage unit 240 may comprise one or more caches (e.g. levelone (L1), level two (L2), and/or level three (L3) caches) fortemporarily storing content, e.g., a Random Access Memory (RAM).Additionally, the data storage unit 240 may comprise a long-term storagefor storing content relatively longer, e.g., a Read Only Memory (ROM).For instance, the cache and the long-term storage may include dynamicrandom access memories (DRAMs), double data rate 3 (DDR3) RAMs and/orsynchronous dynamic random access memories (SDRAMs), solid-state drives(SSDs), hard disks, combinations thereof, or other types ofnon-transitory storage devices.

The radio frequency (RF) interface 220 may be coupled to the processingunit 230 and a radio front end. For example, the radio front end maycomprise one or more antennas and may be configured to receive and/ortransmit radio signals wirelessly. The RF interface 220 may beconfigured to receive digital frames generated by the processing unit230 and transmit the received digital frames to the radio front end.Conversely, the RF interface 220 may be configured to receive digitalframes converted by the radio front end (e.g. from received radiosignals) and transmit the received digital frames to the processing unit230 for processing.

In some embodiments, device 200 may further comprise a power managementsystem, an Ethernet packet switch (e.g. 1 gigabit (G) switch), and/orother system components and may be alternatively configured asdetermined by a person of ordinary skill in the art to achieve the samefunctionalities.

FIG. 3 shows a block diagram of a transmitter 300 for single antennatransmission in accordance with various embodiments. Transmitter 300 maybe employed for generating baseband signals for DL transmissions at a HU(e.g. HU 110) or UL transmissions at a RU (e.g. HU 120) in a wirelessbackhaul system (e.g. system 100) with a single antenna. For example,transmitter 300 may generate baseband signals for UL or DL data channels(e.g. PUSCH or PDSCH). Transmitter 300 may be implemented in aprocessing unit (e.g. processing unit 230), which may comprise one ormore application specific integrated circuits (ASICs), digital signalprocessors (DSPs), and/or hardware accelerators.

Transmitter 300 may comprise an add Cyclic Redundancy Check (CRC) 310component, a RS encoder 321, a byte interleaver 322, a Turbo encoder323, a rate matching 324 component, a channel interleaver 325, and ascrambler 326. The transmitter 300 may be configured to receive an inputdata bit stream for transmission. The transmitter 300 may process theinput data bit stream in units of Media Access Control (MAC) layertransport block (TB). For example, the add CRC 310 component may beconfigured to compute a CRC (e.g. according to a selected CRC generatorpolynomial such as CRC-24) for a MAC TB and may attach the CRC to theend of the MAC TB.

The RS encoder 321 may be coupled to the output of the add CRC 310component and may be configured to perform RS encoding to generate oneor more RS codewords. For example, a RS(255, 255-2T) encoding may beemployed, where T (e.g. T may be about three or about four) mayrepresent the error correction capability (e.g. in bytes) of the RScode. Alternatively, a shortened RS code in the form of RS(255-S,255-2T-S) (e.g. RS(192, 184), RS(128,122), etc.) may be employed, whereS may represent the number of RS symbols for shortening. The byteinterleaver 322 may be coupled to the output of the RS encoder 321 andconfigured to perform byte interleaving across one or more RS codewordsto generate an interleaved frame. The Turbo encoder 323 may be coupledto the output of the RS encoder 321 and may comprise a parallelconcatenated convolutional code (PCCC) generator and an internalinterleaver. The Turbo encoder 323 may be configured to perform Turboencoding to generate one or more Turbo code blocks. In an embodiment,the interleaved frame may be segmented into a plurality of interleavedsub-frames, which may be input to the Turbo encoder 323 such that thebyte interleaving may span across one or more Turbo code blocks.

It should be noted that the structure of the RS encoder 321, the byteinterleaver 322, and the Turbo encoder 323 may be referred to as a FECencoder, where a FEC codeword may comprise one or more Turbo code blocksand each Turbo code block may be generated from multiple RS codewords asdiscussed more fully herein below. The concatenated RS and Turboencoding FEC encoder may be suitable for providing error correctioncapabilities against random and/or bursty channel errors. In someembodiments, a CRC may be added to each FEC codeword (e.g. RS and Turboencoded). In some other embodiments, a CRC may be added to each Turbocode block. In addition, a MAC TB with CRC attachment may be encodedinto an integer number of FEC codewords (e.g. applying concatenatedTurbo and RS codes) discussed more fully below.

The rate matching 324 component may be coupled to the output of theTurbo encoder 323 and may be configured to adjust code rate to match aselected transmission rate. The channel interleaver 325 may be coupledto the output of the rate matching 324 component and may be configuredto perform interleaving, for example, by interleaving the output of therate matching 324 component in units of words, where the number of bitsin each word may correspond to a number of bits in a modulation symbolfor a selected modulation scheme (e.g. four bits for 16-QAM, six bitsfor 64-QAM, eight bits for 256-QAM, etc.). Interleaving may be performedby filling symbols into a matrix by row and then outputting the symbolsin the matrix by column. In an embodiment, the channel interleaver 325may perform interleaving across a number of words that corresponds tothe number of sub-carriers in about two SC-FDMA symbols. It should benoted that the interleaving matrix may be configured with variousdimensions as determined by a person of ordinary skill in the art toachieve the same functionalities. The scrambler 326 may be coupled tothe output of the channel interleaver 325 and may be configured toperform bit-level scrambling according to a selected scramblingsequence.

The transmitter 300 may further comprise a symbol mapper 340, aserial-to-parallel (S/P) conversion 341 component, a DFT 342 component,and a sub-carrier mapper 343. The symbol mapper 340 may be coupled tothe output of the scrambler 326 and may be configured to map thescrambled data bits into modulation symbols according to a selectedmodulation coding scheme (MCS) (e.g. 4, 16, 64, 256-QAM), which may beselected to adapt to channel conditions (e.g. a higher order MCS for ahigher signal-to-noise ratio (SNR) channel). The S/P conversion 341component may be coupled to the output of the symbol mapper 340 and maybe configured to convert the modulated symbols into parallel outputs,which may be inputted into the DFT 342 component. The DFT 342 componentmay be configured to transform the modulated symbols from a time domaininto a frequency domain, where such DFT operation may be referred to asDFT precoding and/or DFT-spreading and may provide frequency diversitygain in a frequency selective channel. The sub-carrier mapper 343 may becoupled to the output of the DFT 342 component and may be configured tomap the DFT outputs onto a plurality of sub-carriers. In someembodiments, the DFT outputs may be mapped to a group of consecutivesub-carriers that span a portion of the system bandwidth or a fullsystem bandwidth. In some other embodiments, the DFT outputs may bemapped to multiple separated portions of the system bandwidth (e.g. neara higher frequency edge or near a lower frequency edge of the systembandwidth). It should be noted that the sub-carrier mapping may bealternatively grouped and/or distributed as determined by a person ofordinary skill in the art to achieve the same functionalities.

The transmitter 300 may further comprise an Inverse Fast FourierTransform (IFFT) 370 component, a parallel-to-serial (P/S) conversion371 component, and an add cyclic prefix (CP) 372 component. The IFFT 370component may be coupled to the output of the sub-carrier mapper 343 andmay be configured to transform the sub-carriers into time domainsamples. In some embodiments, the IFFT 370 component may be configuredwith an additional frequency shift (e.g. or via a frequency shifter) ofabout half a sub-carrier without a phase reset after the frequency shift(e.g. after each SC-FDMA symbol). The P/S conversion 371 component maybe coupled to the output of the IFFT 370 component and may be configuredto convert the IFFT outputs into a block of samples. The add CP 372component may be coupled to the output of the P/S conversion 371component and may be configured to copy a portion of the time domainsamples at the end of the block (e.g. IFFT outputs) to the beginning.The output at the add CP 372 component may be in terms of SC-FDMAsymbols. The SC-FDMA symbols may be transmitted to a radio front end,which may convert the SC-FDMA symbol (e.g. digital time samples) into ananalog RF signal and may transmit the RF signal with a single antennainto air-interface links (e.g. links 130). It should be noted that thestructure of transmitter 300 comprising a symbol mapper 340, followed bythe DFT 342 component, followed by the sub-carrier mapper 343 and theIFFT 370 component may be referred to as a SC-FDMA transmitter. SC-FDMAtransmission scheme may lead to a single-carrier transmit signal withlow PAPR, in contrast to OFDMA, which may be a multiple carriers signalwith higher PAPR.

In some embodiments, transmitter 300 may combine SC-FDMA transmissionwith OFDM transmission. For example, the sub-carrier mapper 343 may beadditionally coupled to other transmission blocks (e.g. encoding and/ormodulation blocks) that generate data for different channels (e.g.control channels) by employing an OFDMA transmission scheme. In suchembodiments, each channel may be mapped to one or more groups ofconsecutive sub-carriers, for example, located at the edges (e.g. near alower frequency edge and near a higher frequency edge) of the systembandwidth or in the middle of the system bandwidth.

FIG. 4 shows a block diagram of a transmitter 400 for rank-1transmission in accordance with various embodiments. Transmitter 400 maybe employed for generating baseband signals for DL transmissions at a HU(e.g. HU 110) or UL transmissions at a RU (e.g. HU 120) in a wirelessbackhaul system (e.g. system 100) with multiple antennas (e.g. about twoantennas or about four antennas) for rank-1 transmission. Transmitter400 may provide improved system performance (e.g. reduced BER) throughspace-frequency transmit diversity when compared to a single antennatransmitter (e.g. transmitter 300). For example, transmitter 400 maygenerate baseband signals for UL and/or DL data channels (e.g. PUSCHand/or PDSCH). Transmitter 400 may be implemented in a processing unit(e.g. processing unit 230), which may comprise one or more ASICs, DSPs,and/or hardware accelerators. Transmitter 400 may comprise an add CRC410 component, a RS encoder 421, a byte interleaver 422, a Turbo encoder423, a rate matching 424 component, a channel interleaver 425, ascrambler 426, a symbol mapper 440, an S/P conversion 441 component, anda DFT 442 component, which may be substantially similar to add CRC 310component, RS encoder 321, byte interleaver 322, Turbo encoder 323, ratematching 324 component, channel interleaver 325, scrambler 326, symbolmapper 340, S/P conversion 341 component, and DFT 342 component,respectively. However, transmitter 400 may further comprise anadditional transmit (Tx) precoder 451 coupled to the output of the DFT442 component.

The Tx precoder 451 may be configured to encode the DFT outputs into twooutput streams by employing a space-frequency block coding (SFBC) scheme(e.g. space frequency Alamouti code) or other precoding scheme fortransmission with multiple antennas (e.g. about two antennas or aboutfour antennas). Transmitter 400 may further comprise two processingchains coupled to the output of the Tx precoder 451 and may beconfigured to process the two precoded streams independently. Eachprocessing chain may comprise a separate sub-carrier mapper 443, an IFFT470 component, a P/S conversion 471 component, and an add CP 472component, which may be substantially similar to sub-carrier mapper 343,IFFT 370 component, P/S conversion 371 component, and add CP 372component, respectively. The block of output samples generated at theoutput of each of the add CP 472 components may be transmitted via aseparate antenna. In some embodiments, transmitter 400 may combineSC-FDMA transmission with OFDM transmission by employing substantiallysimilar mechanisms as in transmitter 300.

FIG. 5 shows a block diagram of a transmitter 500 for rank-2transmission in accordance with various embodiments. Transmitter 500 maybe employed for generating baseband signals for DL transmissions at a HU(e.g. HU 110) or UL transmissions at a RU (e.g. HU 120) in a wirelessbackhaul system (e.g. system 100) with multiple antennas (e.g. about twoantennas or about four antennas) for rank-2 transmission. For example,transmitter 500 may generate baseband signals for UL and/or DL datachannels (e.g. PUSCH and/or PDSCH). Transmitter 500 may be implementedin a processing unit (e.g. processing unit 230), which may comprise oneor more ASICs, DSPs, and/or hardware accelerators. Transmitter 500 maycomprise two separate processing chains with identical structures forbit processing and symbol processing and may encode two separate inputdata bit streams separately. For example, each transmitter chain maycomprise an add CRC 510 component, a RS encoder 521, a byte interleaver522, a Turbo encoder 523, a rate matching 524 component, a channelinterleaver 525, a scrambler 526, a symbol mapper 540, an S/P conversion541 component, and a DFT 542 component, which may be substantiallysimilar to add CRC 310 component, RS encoder 321, byte interleaver 322,Turbo encoder 323, rate matching 324 component, channel interleaver 325,scrambler 326, symbol mapper 340, S/P conversion 341 component, and DFT342 component, respectively. Transmitter 500 may further comprise amultiple-input multiple-output (MIMO) precoder 551 component coupled tothe outputs of the DFT 542 components.

The MIMO precoder 551 component may be configured to encode the twoindependent DFT outputs from each of the DFT 542 component into twooutput streams, for example, via a spatial multiplexing scheme fortransmission with two antennas. In an embodiment, MIMO precoding mayemploy a close loop codebook based method, where a receiver thatreceives the signal transmitted by the transmitter 500 may provide asuitable precoding matrix (e.g. by indicating a precoding matrix index(PMI) selected from a set of pre-determined precoding matrices). Inanother embodiment, a precoding matrix may be determined by exploitingTDD channel reciprocity, where the precoding matrix may be determinedfrom a received signal at a receiving component of a wireless backhaulunit of the transmitter 500 (e.g. a HU 110 may determine a DL precodingmatrix from UL channel estimation). Transmitter 500 may further comprisetwo processing chains coupled to the output of the MIMO precoder 551component and configured to process the two MIMO precoded streamsindependently. Each processing chain may further comprise a sub-carriermapper 560, an IFFT 570 component, a P/S conversion 571 component, andan add CP 572 component, which may be substantially similar tosub-carrier mapper 343, IFFT 370 component, P/S conversion 371component, and add CP 372 component, respectively. The block of outputsamples generated at the output of each of the add CP 572 components maybe transmitted via a separate antenna. In some embodiments, transmitter500 may combine SC-FDMA transmission with OFDM transmission by employingsubstantially similar mechanisms as in transmitter 300.

It should be noted that transmitters 300, 400, and/or 500 may employ aFEC encoding scheme comprising RS encoding (e.g. RS encoder 321, 421,and/or 521), byte interleaving (e.g. byte interleaver 322, 422, and/or522), and Turbo encoding (e.g. Turbo encoder 323, 423, and/or 523) toprovide a lower BER for backhaul communication. Additional performanceimprovements may be achieved by employing a HARQ scheme, where areceiver may provide a transmitter with feedbacks on data receptionstatuses (e.g. positive acknowledgements (ACK) or negativeacknowledgements (NAK)) and the transmitter may retransmit a data packetwhen the receiver fails to receive the data packet successfully (e.g.indicated by a NAK). In some embodiments, a transmitter may manage aplurality of HARQ processes (e.g. different logical channels and/ordifferent receivers) simultaneously and/or may re-transmit data for anumber of times.

FIG. 6 shows a block diagram of a transmitter 600 for DL non-datachannel transmission in accordance with various embodiments. Transmitter600 may be employed for generating baseband signals for DL transmissionsat a HU (e.g. HU 110) in a wireless backhaul system (e.g. system 100)with multiple antennas (e.g. about two antennas or about four antennas)for rank-1 transmission. For example, transmitter 600 may generatebaseband signals for control channels, such as PBCH and/or PDCCH.Transmitter 600 may be implemented in a processing unit (e.g. processingunit 230), which may comprise one or more ASICs, DSPs, and/or hardwareaccelerators. Transmitter 600 may comprise a substantially similarstructure as in transmitter 400, but may employ a different FEC encodingscheme, for example, with RS encoding and/or convolutional encoding..For example, transmitter 600 may comprise an add CRC 610 component, a RSencoder 621, a convolutional encoder 622, a rate matching 624 component,a channel interleaver 625, and a scrambler 626. The add CRC 610component, the RS encoder 621, the rate matching component 624, thechannel interleaver 625, and the scrambler 626 may be substantiallysimilar to add CRC 410 component, RS encoder 421, rate matching 424component, channel interleaver 425, and scrambler 426, respectively. Theconvolutional encoder 622 may be configured to perform convolutionalencoding, for example, with a constraint length of seven and a code rateof ⅓. In some embodiments, the convolutional encoder 622 may performconvolutional encoding with zero tail bits. In some other embodiments,the convolutional encoder 622 may perform convolutional encoding withtail-biting.

In some embodiments, transmitter 600 may employ both RS encoder 621 andconvolutional encoder 622 for FEC encoding or only convolutional encoder622 depending on the size of an input control frame or control message(e.g. PBCH data or PDCCH data). It should be noted that transmitter 600may not employ an interleaver between the RS encoder 621 and theconvolutional encoder 622 since an input control frame may be encodedinto a single RS codeword. In some other embodiments, the RS encoder 621may be replaced with a Bose-Chaudhuri-Hocquengham (BCH) encoder.

Transmitter 600 may further comprise a symbol mapper 640, an S/Pconversion 641 component, and a DFT 642 component, which may besubstantially similar to symbol mapper 440, S/P conversion 441component, and DFT 442 component, respectively. However, symbol mapper640 may be configured to employ a fixed MCS that comprises a lowmodulation order (e.g. Quadrature Phase Shift Keying (QPSK)) to providerobust transmission of control information over noisy channels.

Transmitter 600 may further comprise an SFBC encoder 651 coupled to theoutput of the symbol mapper 640, where the SFBC encoder 651 may besubstantially similar to Tx precoder 451 (e.g. employing an AlamoutiSFBC) and may generate two SFBC encoded streams. Transmitter 600 mayfurther comprise two separate processing chains coupled to the output ofthe SFBC encoder 651 and configured to process the two SFBC encodedstreams. Each processing chain may comprise a sub-carrier mapper 660, anIFFT 670 component, a P/S conversion 671 component, and an add CP 672component, which may be substantially similar to sub-carrier mapper 443,IFFT 470 component, P/S conversion 471 component, and add CP 472component, respectively.

It should be noted that the DFT precoded modulated symbols at the outputof the DFT 642 component may be mapped to one or more groups ofsub-carriers over the system bandwidth. For example, when the input databit stream comprises PBCH data, the DFT output may be mapped to a groupof sub-carriers located in the middle of the system bandwidth. When theinput data bit stream comprises PDCCH data, the DFT output may be mappedto two groups of sub-carriers local at the edges (e.g. near a higherfrequency edge and near a lower frequency edge) of the system bandwidthdiscussed more fully below. In addition, transmitter 600 may employ asame or a different CRC schemes (e.g. CRC-16 with 16-bits in length) atthe add CRC 610 component and/or a same or a different rate matchingschemes at the rate matching 624 component for PBCH data and PDCCH data.

FIG. 7 shows a block diagram of another transmitter 700 for DL non-datachannel transmission in accordance with various embodiments. Transmitter700 may be employed for generating baseband signals for DL transmissionsat a HU (e.g. HU 110) in a wireless backhaul system (e.g. system 100)with two antennas for rank-1 transmission. For example, transmitter 700may generate baseband signals for a control channel, such as a PHICH(e.g. for HARQ processing). Transmitter 700 may be implemented in aprocessing unit (e.g. processing unit 230), which may comprise one ormore ASICs, DSPs, and/or hardware accelerators. Transmitter 700 maycomprise a plurality of processing chains 701, each comprising arepetition 710 component, a Binary Phase Shift Keying (BPSK) modulation720 component, and a spreading 730 component. Each processing chain mayreceive one input data bit, which may indicate a positive acknowledgment(ACK) or a negative acknowledgement (NAK) discussed more fully below.The repetition 710 component may repeat the input data bit, for example,for three times. The BPSK modulation 720 component may be coupled to theoutput of the repetition 710 component and configured to map therepeated data bits into BPSK symbols. The spreading 730 component may becoupled to the output of the BPSK modulation 720 component andconfigured to perform symbol level spreading (e.g. with a factor ofabout four) by employing orthogonal sequences (e.g. eight orthogonalsequences with lengths of about twelve in a frequency domain).

Transmitter 700 may further comprise an adder 740 coupled to the outputsof the plurality of processing chains 701. The adder 740 may beconfigured to add the spread modulation symbols. In some embodiments,the adder 740 may combine up to about eight processing chains 701 (e.g.about eight ACK/NAK bits).

Transmitter 700 may further comprise a scrambler 750, a resource block(RB)-level (e.g. comprising a group of about twelve sub-carriers)repetition 760 component, and a SFBC encoder 751. The scrambler 750 maybe coupled to the output of the adder 740 and may be configured toperform scrambling on the sequence of spread modulation symbolsaccording to a selected scrambling sequence. The RB-level repetition 760component may be coupled to the output of the scrambler 750 andconfigured to perform block-wise repetition on the scrambled symbol. Forexample, each sequence of symbols may be repeated about twice, where onesequence may be mapped to a RB located near a higher frequency edge andthe other sequence may be mapped to a RB located near a lower frequencyedge of a system bandwidth.

The SFBC encoder 751 may be coupled to the output of the RB-levelrepetition 760 component and may be substantially similar to Tx encoder451 and/or SFBC encoder 651. Transmitter 700 may further comprise twoS/P conversion 741 components coupled to the output of the SFBC encoder751 and configured to operate on the two SFBC encoded streams, whereeach of the S/P conversion 741 components may be substantially similarto S/P conversion 441, 541, and/or 641 component.

The outputs at each S/P conversion 741 component may be mapped tosub-carriers for transmission via a substantially similar structure asin transmitter 400 (e.g. through a sub-carrier mapper 443, a IFFT 470component, a P/S conversion 471 component, and an add CP 472 componentfor each output). However, the outputs at the S/P conversion 741component may be mapped to two groups of sub-carriers located near theedges of the system bandwidth (e.g. a higher frequency edge and a lowerfrequency edge) to provide better robustness through frequencydiversity.

It should be noted that transmitters 300, 400, and 500 may be suitablefor generating baseband signals for UL and/or DL data channels, such asPDSCH and/or PUSCH, whereas transmitter 600 may be suitable forgenerating baseband signals for DL control channels, such as PBCH and/orPDCCH, and transmitter 700 may be suitable for generating basebandsignals for DL control channel, such as PHICH. The different datachannels and/or control channels may be time and frequency multiplexedvia sub-carrier mapping (e.g. through sub-carrier mappers 343, 443, 560,and/or 643) according to some selected configurations as discussed morefully below.

In an embodiment, a wireless backhaul system (e.g. system 100) mayemploy carrier aggregation, where a plurality of component carriers (CC)(e.g. combinations of five, ten, and/or twenty MHz frequency bands) maybe employed for transmissions. CCs may be semi-statically configured,where the CCs may be contiguous or non-contiguous, intra-band orinter-band, and each CC may or may not comprise the same bandwidth. Inaddition, UL CC configuration and DL CC configuration may or may not bethe same. In some embodiments, a same transmitter chain (e.g.transmitter 300, 400, 500, 600, and/or 700) may be employed forgenerating and transmitting a signal in each CC.

When employing carrier aggregation, a HU (e.g. HU 110) may allocate oneCC to one RU (e.g. RU 120) and may allocate one or more CCs to each RU.The HU may employ a substantially similar scheduling period (e.g. aboutfive ms or about ten ms) as without carrier aggregation. In anembodiment, a primary CC may carry a PBCH for all CCs and each CC maycarry a PDCCH specific to the CC. In another embodiment, a primary CCmay carry a PBCH for all CCs and each CC may carry a PDCCH and a PUCCHspecific to the CC. When multiple CCs are employed for communicationbetween a HU and a RU, one of the CCs may be a serving CC that servesthe RU. In some embodiments, the serving CC may provide a radio link tothe RU that comprises better performance than other CCs. The serving CCmay also be the CC that the RU first detected during an initial searchand/or employed for initial random access. It should be noted that a HUmay reassign a different serving CC subsequently, for example, for loadbalancing, energy saving, changes in radio link quality, etc. Inaddition, the CC configurations and/or scheduling may be alternativelyconfigured as determined by a person of ordinary skill in the art toachieve the same functionalities.

In an embodiment, a HU (e.g. HU 110) and/or a RU (RU 120) may employsubstantially similar mechanisms for communicating in a UL directionand/or in a DL direction. In such embodiment, a wireless backhaulcommunication unit may comprise a transmitter (e.g. transmitter 300,400, 500, 600, and/or 700) and a receiver with a substantially similarstructure as in the transmitter, but may be in a reverse direction. Forexample, a receiver for receiving a signal generated from a singleantenna transmitter, such as transmitter 300, may comprise a CP removalcomponent, a FFT component, a sub-carrier de-mapper, a frequency domainequalizer, an IDFTcomponent, a channel de-interleaver, a de-scrambler, aTurbo decoder, a byte de-interleaver, a RS decoder, and a CRC removalcomponent.

FIG. 8 shows a block diagram of a transmitter 800 that combines SC-FDMAand Orthogonal Frequency Division Multiplexing (OFDM) transmissions inaccordance with various embodiments. Transmitter 800 may be employed forgenerating baseband signals for DL transmissions at a HU (e.g. HU 110)in a wireless backhaul system (e.g. system 100). Transmitter 800 maycomprises two transmit processing chains 810 and 820, an S/P conversion841 component, a DFT 842 component, an IFFT 870 component, a P/Sconversion 871 component, and an add CP 872 component. The S/Pconversion 841 component, the DFT 842 component, the IFFT 870 component,the P/S conversion 871 component, and the add CP 872 component may besubstantially similar to S/P conversion 341 component, DFT 342component, IFFT 370 component, P/S conversion 371 component, and add CP372 component.

The transmit processing chain 810 may be configured to generate aSC-FDMA baseband signal (e.g. for transporting a PDSCH) and may comprisea substantially similar bit processing (e.g. CRC, FEC, interleaver, andscrambler) and symbols processing (e.g. symbol mapper) structures as intransmitter 300.

The transmit processing chain 820 may be configured to generate an OFDMbaseband signal (e.g. for transporting PHICH) and may comprise asubstantially similar bit processing (e.g. bit-level repetition) andsymbol processing (e.g. BPSK modulation, spreading, adder, and RB levelrepetition) structures as in transmitter 700.

The two transmit processing chains 810 and 820 may generate basebandsignals independently and may be combined by multiplexing in a frequencydomain. For example, the output of the transmit processing chain 810 maybe mapped onto a set of sub-carriers located at about the middle of asystem bandwidth. The output of the transmit processing chain 820 may bemapped onto another set of sub-carrier located near a higher frequencyedge of the system bandwidth and near a lower frequency edge of thesystem bandwidth. Transmitter 800 may provide frequency diversity and asubstantially low PAPR. It should be noted that transmitter 800 may alsobe suitable for rank-1 or rank-2 transmission by employing a structuresubstantially similar to transmitter 400 or 500 at transmit processingchain 810 and may re-configure and/or duplicate the S/P conversion 841component, the DFT 842 component, the IFFT 870 component, the P/Sconversion 871 component, and the add CP 872 component according totransmitters 400 and/or 500.

FIG. 9 shows a block diagram of a wireless backhaul radio frame 900 inaccordance with various embodiments. Radio frame 900 may be employed forUL communication and/or DL communication between a HU (e.g. HU 110) anda plurality of RUs (e.g. RU 120) over wireless backhaul channels (e.g.links 130) in a wireless backhaul system (e.g. system 100). For example,radio frame 900 may be divided into a first sub-frame 910 and a secondsub-frame 920. The first sub-frame 910 may comprise about ten time slots911 (e.g. time slots 0, 1, 2, 3, 4, 6, 7, 8, and 9). Similarly, thesecond sub-frame 920 may comprise about ten time slots 911 (e.g. timeslots 10, 11, 12, 13, 14, 15, 16, 17, 18, and 19). Each time slot 911may comprise about seven SC-FDMA symbols.

In an embodiment, each SC-FDMA symbol may comprise a plurality ofsub-carriers in a system bandwidth of about five MHz, about ten MHz, orabout twenty MHz (e.g. with a guard band), where each sub-carrier maycomprise a spacing of about fifteen kHz. In some embodiments, thesub-carriers in a symbol may be divided into a plurality of RBs (e.g.each comprising about twelve sub-carriers), where each RB may be aminimum unit for resource allocations. For example, each SC-FDMA symbolmay comprise about 1200, about 600, or about 300 sub-carriers for asystem bandwidth of about twenty MHz, about ten MHz, or about five MHz,respectively. Each SC-FDMA symbol may comprise a plurality of timedomain samples, where the sampling rate may be about 30.72 MHz. Eachtime slot 911 may comprise a time interval of about 0.5 ms. For example,each SC-FDMA symbol may comprise a time duration of about 200/3microseconds (us) and a CP with varying lengths, for example, the firstSC-FDMA symbol in each time slot may comprise a CP length of about 160samples and subsequent SC-FDMA symbols in each time slot may comprise aCP length of about 144 samples. As such, each sub-frame 910 and/or 920may comprise a time interval of about five ms, and thus the radio frame900 may comprise a time interval of about ten ms. It should be notedthat the time slot 911 may be referred to as a transmission timeinterval (TTI) and the sub-frame 910 and/or 920 may be referred to as avirtual frame (e.g. for scheduling). In an embodiment, a HU may scheduleDL and/or UL transmissions for RUs in units of time slots 911 (e.g. forexample at least one DL slot and at least one UL slot for each RUregardless of traffic load). In addition, the HU may schedule such thata transition between a DL transmission and a UL transmission occur at aperiodicity of a virtual frame time (e.g. about five ms) or a full radioframe time (e.g. about ten ms) to provide substantially low transmissionlatency.

In an embodiment, a radio frame 900 may comprise a plurality of timeslot types, such as a DL time slot type, a UL time slot type, and/or aspecial time slot type. For example, a time slot 911 of DL time slottype may carry a PDSCH, a PDCCH, and/or a PHICH and may be employed forDL communication from a HU to a RU. A time slot 911 of UL time slot typemay carry a combination of PUSCH and PUCCH and may be employed for ULcommunication from a RU to a HU. A time slot 911 of a special time slottype may carry a PDSCH, a PBCH, a SS, a PRACH, and/or a guard period(GP) and may be employed for UL and/or DL communication between a HU andRUs. It should be noted that the GP in the special time slot may providea silence (e.g. no UL or DL transmission) time interval to split up a DLtransmission and a UL transmission such that a HU and/or a RU may switchbetween a transmitting mode and a receiving mode.

The time slots 911 may carry the different channels by employing a timeand/or frequency multiplexing scheme as discussed more fully hereinbelow. The time slots 911 in radio frame 900 may be generated andtransmitted by employing one or more transmitters, such as transmitters300, 400, 500, 600, 700, and/or 800. For example, transmitter 300employing a single antenna transmission scheme may transmit about oneMAC layer TB per TTI, transmitter 400 employing rank-1 transmissionscheme may transmit about one MAC layer TB per TTI, and transmitter 500employing a rank-2 transmission scheme may transmit about two MAC layerTBs per TTI.

FIG. 10 shows a block diagram of a DL slot 1000 in accordance withvarious embodiments. The DL slot 1000 may be employed for DLcommunication between a HU (e.g. HU 110) and a RU (e.g. RU 120) over awireless backhaul link (e.g. link 130) in a wireless backhaul system(e.g. system 100) and may correspond to a time slot (e.g. time slot 911)in a radio frame (e.g. radio frame 900). The DL slot 1000 may comprise aplurality of symbols (e.g. about seven symbols) in time (e.g. depictedin the x-axis) and a plurality of sub-carriers in frequency (e.g.depicted in the y-axis). The number of sub-carriers may vary dependingon the system bandwidth employed between the HU and the RU. For example,the number of sub-carriers may be about 1200, about 600, or about 300for a system bandwidth of about twenty MHz, about ten MHz, or about fiveMHz, respectively. The DL slot 1000 may comprise a PDSCH block 1010, aPS block 1020, and a PHICH block 1030 multiplex in frequency and intime.

In an embodiment, the PS block 1020 may be located at about symbol threein DL slot 1000 and may span all sub-carriers of symbol three. The PSblock 1020 may carry a predetermined pilot sequence, such as a randomConstant Amplitude Zero AutoCorrelation (CAZAC) sequence, a Zadoff-Chusequence, or any other sequence that comprises signal propertiessuitable for distinguishing from other signals in the wireless backhaullinks as determined by a person of ordinary skill in the art. The pilotsequence may be symbol mapped and transmitted during symbol three by atransmitter substantially similar to transmitter 300, 400, and/or 500,for example, inserting a PS generation unit located at the input to thesub-carrier mapper 343, 443, and/or 560, respectively. In someembodiments of transmitters with multiple antennas, a cyclic shiftedversion of the pilot sequence may be transmitted at one of the antennas.The PS block 1020 may allow a receiver at a RU (e.g. RU 120) to detectslot boundaries, estimate carrier frequency offset (CFO) and/or symboltiming, perform channel estimate, etc. It should be noted that transmitprecoding and sequence hopping may not be applied to transmission of PSblock 1020. It should be noted that such configuration of the PS block1020 at about the middle of a DL slot 1000 may provide better PHYperformance in a time varying channel environment since each symbol inthe DL slot 1000 may comprise a smaller time difference from the PSblock 1020, and thus may lead to less change and/or drift in channelestimation at a corresponding receiver.

In an embodiment, the PHICH blocks 1030 may be located at about symbolfour (e.g. after PS block 1020) in time and near the two extreme edges(e.g. about 24 sub-carriers near a higher frequency edge and about 24sub-carriers near a lower frequency edge) of the system bandwidth. ThePHICH blocks 1030 may carry acknowledgements for UL data transfers (e.g.received in previous UL slots). The acknowledgements may be indicated byabout one bit, which may be termed as an ACK bit when the UL data isreceived successfully or a NAK bit when the UL data is receivedunsuccessfully. Multiple acknowledgements (e.g. up to about eightACK/NAK bits) may be carried in a same RB by employing differentorthogonal cover sequences and may be referred to as a PHICH group. Forexample, the PHICH blocks 1030 may span about two RBs at each spectrumedge and may carry about one or two PHICH groups. The PHICH blocks 1030may be generated and transmitted by employing a transmitter, such astransmitter 700. It should be noted that each PHICH group may be carriedin two RBs, one on each frequency edge of the system frequency band(e.g. via RB-level repetition 760 component) to improve robustness viafrequency diversity.

In an embodiment, the PDSCH block 1010 may be located at symbols zero,one, two, four, five, and/or six in DL slot 1000 and may span allsub-carriers except the sub-carriers carrying the PHICH blocks 1030(e.g. via frequency multiplexing). The PDSCH block 1010 may carry DLdata destined for a particular RU. The PDSCH block 1010 may be generatedand transmitted by employing a transmitter, such as transmitter 300,400, and/or 500.

FIG. 11 shows another block diagram of a DL slot 1100 in accordance withvarious embodiments. The DL slot 1100 may be employed for DLcommunication between a HU (e.g. HU 110) and a RU (e.g. RU 120) over awireless backhaul link (e.g. link 130) in a wireless backhaul system(e.g. system 100) and may correspond to a time slot (e.g. time slot 911)in a radio frame (e.g. radio frame 900). The DL slot 1100 may comprise asubstantially similar time-frequency structure as in DL slot 1000, butmay comprise different contents. For example, DL slot 1100 may comprisea PDSCH block 1110, a PS block 1120, and a PHICH block 1130, which maybe substantially similar to PDSCH block 1010, PS block 1020, and PHICHblocks 1030, respectively. However, DL slot 1100 may comprise additionalPDCCH blocks 1140 multiplex in time and in frequency with the PDSCHblock 1110, the PS block 1120, and the PHICH blocks 1130.

In an embodiment, the PDCCH blocks 1140 may be located at about symboltwo (e.g. before the PS block 1120) in time and near the two extremeedges (e.g. about 120 sub-carriers at a higher frequency edge and about120 sub-carriers at a lower frequency edge) of the system frequencyband. The PDCCH blocks 1140 may carry physical layer controlinformation, which may be per link and may be specific to a RU. Forexample, DL slot 1100 may be assigned to a specific RU, where the PDCCHblocks 1140 may comprise a physical layer transmission control and/orconfiguration for the DL slot 1100 and/or subsequent DL slots if the RUis assigned with multiple DL slots. In addition, the PDCCH blocks 1140may carry a physical layer transmission control and/or configuration forone or more next UL slots assigned to the RU in a scheduling period.Some examples of physical layer transmission control may include a MCSconfiguration, a MIMO configuration, a UL power control command, a HARQprocess number (e.g. for identifying a HARQ logical channel), a HARQredundancy version (RV) number (e.g. for identifying a re-transmissiondata), etc. The PDCCH blocks 1140 may be generated and transmitted byemploying a transmitter, such as transmitter 600. It should be notedthat the physical layer transmisison control and/or configurations forthe DL transmission and the UL transmission may be combined (e.g. bymultiplexing and/or concatenating) before processing by the transmitter600.

FIG. 12 shows a block diagram of a special slot 1200 in accordance withvarious embodiments. The special slot 1200 may be employed for DLcommunication between a HU (e.g. HU 110) and a RU (e.g. RU 120) over awireless backhaul link (e.g. link 130) in a wireless backhaul system(e.g. system 100) and may correspond to a time slot (e.g. time slot 911)in a radio frame (e.g. radio frame 900). The special slot 1200 maycomprise a substantially similar time-frequency structure as in DL slot1100, but may comprise different contents. For example, the special slot1200 may comprise a PDSCH block 1210, a PS block 1220, a PBCH block1250, and a GP block 1260 multiplex in time and in frequency. The PDSCHblock 1210 and the PS block 1220 may be substantially similar to PDSCHblock 1110 and PS block 1120, respectively. However, the PDSCH block1210 may carry DL data for a RU continuing from a previous PDSCH block(e.g. PDSCH block 1010 or 1110) in a previous DL slot (e.g. slot 1000and/or 1100). The PDSCH block 1210 may be transmitted by employing thesame transmission configuration as in the previous DL slot. It should benoted that the PDSCH block 1210 may not be a standalone allocation to aRU (e.g. special slot 1200 may not carry a PDCCH block, such as PDCCHblock 1140).

In an embodiment, the PBCH block 1250 may be located at about symbolsone and two in special slot 1200 and may span a fixed number ofsub-carriers (e.g. about 300 sub-carriers spanning a five MHz bandwidthin each symbol) centered around the direct current (DC) sub-carrierregardless of the system bandwidth. The PBCH block 1250 may carry systeminformation, such as frame number, system bandwidth, transmissionschedule, PRACH configurations and parameters, etc. The transmissionschedule may include slot assignments (e.g. both UL and DL assignments)for the RUs in a next sub-frame. The PBCH block 1250 may be generatedand transmitted by employing a transmitter, such as transmitter 600, andmay be frequency multiplexed (e.g. via sub-carrier mapping) with PDSCHblock 1210 in the same symbol.

In an embodiment, the GP block 1260 may be located at about symbol fourin special slot 1200. The GP block 1260 may be a silence time interval(e.g. no UL or DL transmission) to allow transmission directions to beswitched (e.g. from a DL direction to a UL direction). It should benoted that in some embodiments, RUs may be synchronized to the HU in aUL direction and may switch from a receiving mode to a transmitting modeduring the time interval of the GP block 1260. It should be noted thatsymbols five and six may be un-allocated in special slot 1200.

FIG. 13 shows a block diagram of another special slot 1300 in accordancewith various embodiments. The special slot 1300 may be employed for DLand/or UL communication between a HU (e.g. HU 110) and a RU (e.g. RU120) over a wireless backhaul link (e.g. link 130) in a wirelessbackhaul system (e.g. system 100) and may correspond to a time slot(e.g. time slot 911) in a radio frame (e.g. radio frame 900). Thespecial slot 1300 may comprise a substantially similar slot structure asin special slot 1200. However, the special slot 1300 may comprise anadditional time interval for UL transmission. For example, the specialslot 1300 may comprise a PDSCH block 1310, a PS block 1320, a PBCH block1350, and a GP block 1360, which may be substantially similar to PDSCHblock 1210, PS block 1220, PBCH block 1250, and GP block 1260,respectively. The special slot 1300 may further comprise a SS block 1370and a PRACH block 1380.

In an embodiment, the SS block 1370 may be located at about symbol zeroin special slot 1300 and may span a fixed number of sub-carriers (e.g.about 300 sub-carriers occupying five MHz) centered around the directcurrent (DC) sub-carrier regardless of the system bandwidth. The SSblock 1370 may carry a predetermined synchronization sequence, such as arandom CAZAC sequence or any other sequence that comprises signalproperties (e.g. randomness, correlation property, etc.) suitable fordistinguishing from other signals in the wireless backhaul links asdetermined by a person of ordinary skill in the art. In someembodiments, a wireless backhaul system may employ about seven uniqueCAZAC sequences for about seven different cell clusters (e.g.geographically divided areas). The synchronization sequence may bemapped to modulation symbols and transmitted during symbol zero by atransmitter substantially similar to transmitter 300, 400, and/or 500,for example, inserting a SS generation unit located at the input to thesub-carrier mapper 343, 443, and/or 560, respectively. It should benoted that the same synchronization sequence may be transmitted at eachantenna when the transmitter comprises multiple antennas. In someembodiments, the SS block 1370 may be transmitted with frequencyshifting (e.g. by about half a sub-carrier frequency). The SS block 1370may allow a receiver at a RU to search for and/or synchronize to a HUduring initial link setup, estimate initial CFO, etc. For example, theSS block 1370 may be transmitted about once per radio frame.

In an embodiment, the PRACH block 1380 may span about two symbols (e.g.located at about symbols five and six) in time and a plurality ofsub-carriers. The PRACH block 1380 may be transmitted by a RU to a HUduring initial link access. The PRACH block 1380 may carry apredetermined random preamble sequence, such as a logical root sequence,a physical root sequence, a cyclic shift sequence generated from asingle root Zadoff-Chu sequence (e.g. with a length N_zc of 139 andcyclic shift N_cs of 15), or another sequence that comprises signalproperties suitable for random access as determined by a person ofordinary skill in the art. In an embodiment, when the random preamblesequence is a Zadoff-Chu sequence, for example, with a length of about139 and a cyclic shift number of about 15, such embodiment may allownine different sequences for random access in a cell.

The random preamble sequence may be symbol mapped and transmitted duringsymbol three by a transmitter substantially similar to transmitter 300,400, and/or 500, for example, by inserting a PRACH generation unitlocated at the input to the sub-carrier mapper 343, 443, and/or 560. Inan embodiment, the PRACH block 1380 may comprise a sub-carrier spacingof about 7.5 kHz (e.g. narrower than other physical channels) and therandom preamble sequence may be mapped to about six RBs and split intotwo frequency edges with a frequency guard band of about fivesub-carriers. In an embodiment, the PRACH block 1380 may comprise a timestructure comprising a sequence length of about 4096 samples, a CPlength of about 448 samples, and a guard period (e.g. to accommodatetiming uncertainties during initial access) length of about 288 samples.The PRACH block 1380 may allow a receiver at the HU to measure initialtiming adjustment during the initial link setup. It should be noted thatthe generation and transmission of the PRACH block 1380 may beconfigured by an upper network layer (e.g. Open System Interconnection(OSI) model layers), such as a MAC layer, and the configurationparameters (e.g. random preamble sequence index, etc.) may be carried ina PBCH block (e.g. PBCH block 1350).

FIG. 14A shows a block diagram of a UL slot 1400 in accordance withvarious embodiments. The UL slot 1400 may be employed for ULcommunication between a HU (e.g. HU 110) and a RU (e.g. RU 120) over awireless backhaul link (e.g. link 130) in a wireless backhaul system(e.g. system 100) and may correspond to a time slot (e.g. time slot 911)in a radio frame (e.g. radio frame 900). The UL slot 1400 may comprise asubstantially similar time-frequency structure as in DL slot 1100, butmay comprise different content. For example, UL slot 1400 may comprise aPUSCH block 1410, a PS block 1420, and a PUCCH block 1430 multiplex intime and in frequency. The PUSCH block 1410 and the PS block 1420 may besubstantially similar to PDSCH block 1110 and PS block 1120. However,the PUSCH block 1410 may be employed for UL data transfer (e.g. from aRU to a HU) instead of DL data transfer as in PDSCH block 1110.

In an embodiment, the PUCCH block 1430 may be located at the two extremefrequency edges (e.g. a higher frequency edge and a lower frequencyedge) of the system bandwidth across all symbols in UL slot 1400. ThePUCCH block 1430 may carry layer I /layer 2 (e.g. OSI layers) signaling,which may include reports for ACK/NAK, CQI, RI, Scheduling Request (SR),etc. The PUCCH block 1430 may be generated and transmitted by employinga transmitter substantially similar to transmitter 300, 400, and/or 500,for example, by inserting a report generation unit at the input to thechannel interleaver 325, 425, and/or 525, respectively.

A more detailed view of the frequency mapping of the PUCCH block 1430 ofthe UL slot 1400 is illustrated in FIG. 14B as UL slot 1490. UL slot1490 may comprise a substantially similar time-frequency structure as inUL slot 1400, but may represent frequencies in the y-axis in units ofRBs (e.g. each comprising about twelve sub-carriers) instead ofsub-carriers. UL slot 1490 may comprise a set of RBs (m=0) 1491, (m=1)1492, and (m=2) 1493, where each set of the RBs may comprise a sub-setof RBs located near a higher frequency edge of the system bandwidth andanother sub-set of RBs located near a lower frequency edge of the systembandwidth and may be symmetric about a DC sub-carrier (e.g. about samenumber of RBs from about the DC sub-carrier). Each set of the RBs maycarry a PUCCH block 1430 generated by a different RU (e.g. RU 120). Inan embodiment, a RU may be configured with an upper layer PUCCH mappingconfiguration parameter and may determine locations for the set of RBsfrom the upper layer PUCCH mapping configuration parameters.

FIGS. 15A/B shows a block diagram of a wireless backhaul radio sub-frame1500 in accordance with various embodiments. The radio sub-frame 1500may comprise a substantially similar time-frequency structure as inradio frame 900. However, the radio sub-frame 1500 may comprise half thenumber of time slots 911 (e.g. about ten) in radio frame 900. The radiosub-frame 1500 may be employed for UL communication and/or DLcommunication between a HU (e.g. HU 110) and a plurality of RUs (e.g. RU120) over wireless backhaul channels (e.g. links 130) in a wirelessbackhaul system (e.g. system 100).

The radio sub-frame 1500 may comprise a plurality of DL slots 1510 (e.g.slots 1000) and 1520 (e.g. slots 1100), a special slot 1530 (e.g. slot1300), and a plurality of UL slots 1540 (e.g. slots 1400). As shown inFIGS. 15A/B, the radio sub-frame 1500 may be configured such that the DLslots 1510 and/or 1520 may be grouped together, the UL slots 1540 may begrouped together, and the special slot 1530 separates the DL slots 1510and 1520 from the UL slots 1540, where a DL-UL transition may occurduring a guard period in the special slot 1530 as discussed hereinabove. It should be noted that the boundary between a UL to DLtransition may be adjustable for traffic load balancing.

Radio sub-frame 1500 may be configured such that a RU may be assignedwith more than one time slot for transmitting in a DL direction, forexample, a DL slot 1520 may be followed by one or more DL slots 1510. Itshould be noted that the first assigned slot (e.g. DL slot 1520) maycarry a PDCCH (e.g. PDCCH block 1140) to indicate a physical layertransmission control employed for transmitting the first assigned slot,whereas subsequent assigned slots may not carry a PDCCH and may employthe same physical layer transmission control as the first assigned slotindicated in the PDCCH.

In an embodiment, a radio frame (e.g. radio frame 900 and/or radiosub-frame 1500) may be configured with a DL-UL switching period of abouthalf a frame. In such a frame configuration, two special slots may bescheduled in the radio frame separated by half a frame (e.g. about tentime slots 911) as each special slot may include a GP (e.g. GP block1260) for DL-UL transition and a PBCH for providing transmissionschedules. In addition, a PRACH may be included in a radio frame, wherethe PRACH density may be low and may be indicated in the PBCH. As such,a radio frame may comprise one special slot without PRACH (e.g. specialslot 1200) and one special slot with PRACH (e.g. special slot 1300)separated by half a frame in the radio frame. The number of DL slots andUL slots in a radio frame may be adjusted based on traffic load and thenumber of RUs (e.g. RU 120) in the wireless backhaul system (e.g. system100).

In an embodiment, a radio frame (e.g. radio frame 900 and/or radiosub-frame 1500) may be configured such that each DL slots (e.g. DL slots1000 and/or 1100), UL slots (e.g. UL slots 1400), and/or special slots(e.g. special slots 1200 and/or 1300) may comprise a PS (e.g. PS block1020, 1120, 1320, and/or 1420) at about the first symbol of thecorresponding slot to provide a low receive processing delay at acorresponding receiver. For example, the receiver may compute a channelestimate after receiving the PS at the first symbol and may employ thechannel estimate for decoding subsequent symbols in the correspondingtime slot. In addition, a DL slot may comprise a PDCCH block (e.g. PDCCHblock 1140) and a PHICH block (e.g. PHICH block 1030 and/or 1130)located in a same symbol (e.g. at about a second symbol in the DL slot)by frequency multiplexing. For example, the PDCCH block may be mappedonto a first set of sub-carriers located near a lower frequency edge anda second set of the sub-carriers located near a higher frequency edge ofa system bandwidth. Similarly, the PHICH block may be mapped to a thirdset of sub-carriers located near a lower frequency edge and a fourth setof sub-carriers located near a higher frequency edge of a systembandwidth. The first set of sub-carriers may be located at lowerfrequencies than the third set of sub-carriers and the second set ofsub-carriers may be located at higher frequencies than the fourth set ofsub-carriers.

FIGS. 16 and 17 illustrate an embodiment of UL-DL slot configurationsfor a radio frame (e.g. radio frame 900) and may denote a UL slot by U,a DL slot by D, and a special slot by S. FIG. 16 shows tables 1610 and1620 of slot configurations in accordance with various embodiments.Table 1610 shows a plurality of first slot configurations for a firsthalf (e.g. sub-frame 910 and/or 1500) of a ten ms radio frame (e.g.radio frame 900) and Table 1620 shows a plurality of second slotconfigurations for a second half (e.g. sub-frame 920 and/or 1500) of aradio frame. As shown in Tables 1610 and 1620, special slots may belocated at specific slot locations that are fixed across radio frames,for example, at slot two in the first sub-frame and in slot twelve forthe second sub-frame. It should be noted that switching from a DL slotto a UL slot may occur at the special slot as discussed more fullybelow. As such, the slot configurations shown in Tables 1610 and 1620may provide a DL-UL switching period of about half a radio frame. Aradio frame may be configured by combining a slot configuration selectedfrom Table 1610 for a first sub-frame and a slot configuration selectedfrom Table 1620 for a second sub-frame. However, some combinations mayresult in the same DL ratios and the same UL slot ratios. It should benoted that the slot configurations, the specific locations of thespecial slots, and/or the DL-UL switching period may be alternativelyconfigured as determined by a person of ordinary skill in the art toachieve the same functionalities.

FIG. 17 shows a table 1700 of UL-DL slot configurations andcorresponding DL ratios and UL ratios in accordance with variousembodiments. For example, the slot configurations in Table 1700 areformed from selected combinations of the slot configurations from Table1610 and Table 1620, where the DL ratios may vary from about 26 percent(%) to about 89% and the UL ratios may vary from about 74% to about 11%accordingly. It should be noted that the UL-DL slot configurations maybe configured with various configurations and may be alternativelyconfigured as determined by a person of ordinary skill in the art toachieve the same functionalities.

In an embodiment, transmission latency may be defined as the timeduration from a packet being available at an Internet Protocol (IP)layer at a HU (e.g. HU 110) or a RU (e.g. RU 120) and the availabilityof the packet at an IP layer at a RU or a HU, respectively. Transmissionlatency may include a processing delay at a transmitter, TTI duration,frame alignment delay, and/or processing delay at a receiver. Theprocessing delay at the transmitter (e.g. about 0.5 ms), the TTIduration (e.g. about 0.5 ms), and/or the processing delay at thereceiver (e.g. about 1.0 ms) may be independent of slot configurationsand may be substantially constant, whereas the frame alignment delay mayvary depending on the slot configurations. For example, the longest DLtransmission latency (e.g. about 4.05 ms) may occur when a schedulingperiod (e.g. about five ms) comprises only one DL slot and the longestUL transmission latency (e.g. about 4.5 ms) may occur when a schedulingperiod comprises only one UL slot. As such, when the scheduling periodis about five ms, the transmission latency may be less than about fivems.

In an embodiment of a HARQ scheme, a HARQ feedback (e.g. ACK/NAK) for adata packet received in a time slot (e.g. slot n) may be sent in a nextgranted time slot that is at least about eight time slots later (e.g.slot n+8). As such, the HARQ feedback timing may vary depending on theslot configurations. For example, when the slot configuration, such asTable 1700, is employed, the HARQ feedback timing may vary between abouteight to about seventeen time slots (e.g. about 4 ms to about 8.5 ms).It should be noted that retransmission rate may be substantially lowwhen employing a FEC scheme comprising concatenated RS encoding andTurbo encoding, and thus the additional HARQ delay may be expected tooccur at a substantially low rate.

FIG. 18 shows a block diagram of a FEC encoding method 1800 for encodingPDSCH and/or PUSCH data in accordance with various embodiments. Method1800 may be implemented at a transmitter (e.g. transmitter 300, 400,500, and/or transmit processing chain 810) located at a HU (e.g. HU 110)and/or a RU (e.g. RU 120). Method 1800 may begin with receiving a MAC TB1871 (e.g. about 2205 bytes in length) at step 1810. At step 1820,method 1800 may append a CRC (e.g. about 3 bytes in length) to the MACTB 1871 to generate a CRC-appended TB 1872 (e.g. about 2208 bytes inlength). At step 1830, method 1800 may RS encode (e.g. by employing aRS(192, 184) code at a RS encoder 321, 421, and/or 521) the CRC-appendedTB 1872 into a plurality of RS codewords 1873 (e.g. about 192 bytes inlength). At step 1840, method 1800 may byte interleave (e.g. byemploying a byte interleaver 322, 422, and/or 522) across a group of theRS codewords 1873 (e.g. about six RS codewords) to generate aninterleaved frame 1874 and may additionally segment the interleavedframe 1874 into a plurality of interleaved sub-frames 1875 (e.g. aboutthree sub-frames of about 384 bytes length), where each sub-frame 1875may be encoded by a Turbo encoder (e.g. Turbo encoder 323, 423, and/or523). It should be noted that the size of the group of RS codewords forbyte interleaving and the number of interleaved sub-frames may vary andmay be determined according to the size of the MAC TB 1871. However, theFEC encoding may be configured such that each Turbo encoder input maycomprise multiple RS codewords 1873 to provide error correctioncapabilities against bursty channel errors.

FIG. 19 shows a flowchart of an FEC encoding method 1900 in accordancewith various embodiments. Method 1900 may be implemented at atransmitter (e.g. transmitter 300, 400, and/or 500) located at a HU(e.g. HU 110) and/or a RU (e.g. RU 120) during FEC encoding of PDSCHand/or PUSCH data as described in method 1800. For example, method 1900may begin with receiving a MAC TB at step 1910. For example, the MAC TBmay comprise a length of about 2205 bytes. At step 1920, method 1900 maycompute a CRC for the MAC TB and may append the computed CRC at the endof the MAC TB. For example, the CRC may be a CRC-24, which may compriseabout three bytes. Thus, the CRC appended MAC TB may be about 2208 bytesin length. At step 1930, method 1900 may divide the CRC appended MAC TBinto a plurality of sub-blocks (e.g. about twelve sub-blocks of about184 bytes). At step 1940, method 1900 may RS encode each sub-block, forexample, by employing a RS(192, 184) code, and thus may generate a RSencoded block of about 192 bytes from each sub-block. At step 1950,method 1900 may byte interleave across a plurality of the RS encodeblocks (e.g. about six RS encoded blocks). For example, method 1900 maybyte interleave the first six RS encoded blocks and then byte interleavethe second six encoded blocks to generate about two interleaved blocksfrom the RS encoded blocks. At step 1960, method 1900 may divide eachinterleave block into a plurality of interleaved sub-blocks (e.g. aboutthree interleaved sub-blocks of about 384 bytes). At step 1970, method1900 may Turbo encode each interleaved sub-block.

The concatenating of RS encoding and Turbo encoding in method 1900 mayprovide error correction capability against bursty channel errors at areceiver. For example, a Turbo decoder at a receiver may fail to decodeand correct bursty channel errors, but subsequent RS decoding at a RSdecoder may correct the bursty errors. In addition, the encoding of themultiple RS codewords into multiple Turbo code blocks may provideadditional error correction capability, where bursty errors may bespread across multiple RS codewords, thus improving system performance(e.g. lower BER). It should be noted that the CRC scheme, the adding ofthe CRC (e.g. per MAC TB block, Turbo code block, or FEC codeword), theRS code, the number of RS sub-blocks, the number of interleaving blocks,and/or the number of Turbo code blocks may be alternatively configuredas determined by a person of ordinary skill in the art to achieve thesame functionalities.

FIG. 20 shows a flowchart of a method 2000 for initial random access inaccordance with various embodiments. Method 2000 may be implemented at aRU (e.g. RU 120) during initial setup. Method 2000 may begin withdetecting a SS in a received signal at step 2010. Upon detecting a SS inthe received signal, method 2000 may proceed to step 2020. As describedearlier, SS may be carried in a special slot (e.g. special slot 1300),which may be transmitted once per radio frame (e.g. radio frame 900and/or 1500). In addition, a special slot may carry PBCH data and a PS.Thus, at step 2020, method 2000 may determine a half frame boundaryand/or PBCH location, estimate channel from the PS, and decode the PBCHdata. For example, method 2000 may determine system information and/orPRACH configuration from the PBCH data. Some examples of systeminformation and/or PRACH configuration may include bandwidthconfiguration, antenna configuration, frame configuration (e.g. five msor ten ms duration), a sub-frame number, slot configurations (e.g. UL orDL), PRACH opportunities (e.g. a PRACH time) and/or parameters (e.g.root sequence), PS root sequences, etc.

At step 2030, method 2000 may wait for the PRACH time indicated in thedecoded PBCH data. When the PRACH time arrives, method 2000 may proceedto step 2040 to send a random preamble sequence according to PRACHconfiguration at the PRACH time. After sending the random preamblesequence, method 2000 may wait for a next PBCH at step 2050.

Upon receiving a next PBCH, method 2000 may proceed to step 2060. Atstep 2060, method 2000 may decode the PBCH data to retrieve slotassignments. At step 2070, method 2000 may determine whether a DL slotis granted to the RU. If a DL slot is granted, the initial random accessprocedure is completed and other UL timing adjustments and/or link setupprocedure may be performed subsequent to the initial random accessprocedure. If a DL is not granted at step 2070, method 2000 may returnto step 2030 to wait for a next PRACH time and repeat the random accessprocedure in the loop of steps 2030 to 2070. It should be noted that anunsuccessful random access may be caused by collisions.

It should be noted that the disclosed TDD radio frame configurations andbaseband generation schemes may also be employed using FDMA schedulinginstead of TDMA scheduling. However, TDMA scheduling may provide bettersystem performance (e.g. lower BER) than FDMA scheduling.

The above discussion is meant to be illustrative of the principles andvarious embodiments of the present invention. Numerous variations andmodifications will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such variations and modifications.

What is claimed is:
 1. A method for communicating over a wirelessbackhaul channel, comprising: generating a radio frame comprising aplurality of time slots, wherein each time slot comprises a plurality ofsymbols in time and a plurality of sub-carriers in a system bandwidth,and wherein the radio frame comprises an adjustable link directionalityratio of a number of the time slots for an uplink (UL) direction and thenumber of time slots for a downlink (DL) direction to provide trafficload balancing; broadcasting a broadcast channel signal to a pluralityof remote units in a number of consecutive sub-carriers centered about adirect current (DC) sub-carrier in at least one of the time slots in theradio frame regardless of the system bandwidth, wherein the broadcastchannel signal comprises a transmission schedule comprising slotassignments that indicate a link direction and a transmissionopportunity for a first of the plurality of remote units; andtransmitting a DL control channel signal and a DL data channel signal tothe first remote unit, wherein the DL control channel signal comprisesDL control information that controls transmission of the DL data channelsignal, wherein the broadcast channel signal, the DL control channelsignal, and the DL data channel signal are transmitted by employing atime-frequency multiplex scheme, and wherein the DL data channel signalis transmitted by employing a single carrier block transmission schemecomprising a Discrete Fourier Transform (DFT) spreading for frequencydiversity.
 2. The method of claim 1, wherein each time slot comprises afixed time duration, and wherein the transmission schedule comprises ascheduling period about a half radio frame time duration or a full radioframe time duration.
 3. The method of claim 2, wherein the fixed timeduration comprises about 0.5 milliseconds (ms) to provide lowtransmission latency, and wherein the radio frame comprises about twentytime slots.
 4. The method of claim 1 further comprising transmitting apilot sequence (PS) in a symbol time spanning all the sub-carriers inthe system bandwidth, wherein the PS comprises a pre-determined sequencecomprising signal properties that provide channel estimationcapabilities in the system bandwidth.
 5. The method of claim 4, whereinthe PS is transmitted at a beginning of each time slot assigned for theDL direction to provide low receive processing latency at the remoteunits.
 6. The method of claim 4, wherein the PS is transmitted at abouta middle of each time slot assigned for the DL direction to providechannel estimation with low timing drift in a time-varying channel. 7.The method of claim 1, wherein the radio frame comprises at least onespecific time slot comprising a DL time period, a guard time period toprovide a link direction switching opportunity, and an UL time period toprovide an UL random access opportunity, and wherein the broadcastchannel signal is broadcasted in the DL time period of the specific timeslot.
 8. The method of claim 7, wherein the DL time period comprisesabout four symbols, wherein the guard time period comprises about onesymbol, and wherein the UL time period comprises about two symbols. 9.The method of claim 7, wherein the specific time slot is located atabout a third time slot in the radio frame, at about a thirteenth timeslot in the radio frame, or combinations thereof.
 10. The method ofclaim 7 further comprising transmitting a synchronization sequence (SS)in a same set of sub-carriers as the broadcast channel signal in the DLtime period of the specific time slot by time multiplexing with thebroadcast channel signal, wherein the SS comprises a pre-determinedsequence comprising signal properties that provide signal detectioncapabilities for identifying the radio frame.
 11. The method of claim10, wherein the SS sequence is transmitted in about one symbol time, andwherein the broadcast channel signal is transmitted in about two symboltime.
 12. The method of claim 1, wherein the broadcast channel signaland the DL control channel signal are transmitted by employing thesingle carrier block transmission scheme.
 13. The method of claim 1,wherein the DL control channel signal is transmitted in a first set ofthe sub-carriers located near a higher frequency edge of the systembandwidth and a second set of the sub-carriers located near a lowerfrequency edge of the system bandwidth.
 14. The method of claim 1,wherein the slot assignments comprise a slot assignment for the firstremote unit for UL transmission, wherein the DL control channel signalfurther comprises UL control information for the UL transmission, andwherein the method further comprises: combining at least some of the DLcontrol information and at least some of the UL control information togenerate a control frame; and computing a Cyclic Redundancy Check (CRC)for the control frame.
 15. The method of claim 1 further comprising:receiving a UL data channel signal comprising a UL data frame from thefirst remote unit; generating a hybrid automatic repeat request (HARQ)feedback signal according to a reception status of the UL data frame;mapping the HARQ feedback signal to a first set of the sub-carrierslocated near a higher frequency edge of the system bandwidth; andrepeating the mapping of the HARQ feedback signal to a second set of thesub-carriers located near a lower frequency edge of the systembandwidth.
 16. An apparatus, comprising: a processing resourceconfigured to: perform single carrier modulation on a plurality of databit streams to generate a plurality of Single Carrier-Frequency DivisionMultiple Access (SC-FDMA) frames, wherein to perform the single carriermodulation on each data bit stream, the processing resource is to:perform symbol mapping on each data bit stream to generate a pluralityof modulated data symbols; and perform Discrete Fourier Transform (DFT)precoding on the modulated data symbols; and perform frequency-timemultiplexing to combine at least one of the SC-FDMA frames with anOrthogonal Frequency Division Multiplexing (OFDM) frame to generate adigital radio frame; and a radio front end interface coupled to theprocessing resource and configured to cause the digital radio frame tobe transmitted to a wireless backhaul remote unit.
 17. The apparatus ofclaim 16, wherein the data bit streams comprise a broadcast channel databit stream and a downlink (DL) control channel bit stream, wherein thebroadcast channel bit stream is symbol mapped according to a first fixedmodulation coding scheme (MCS), and wherein the DL control channel bitstream is symbol mapped according to a second fixed MCS.
 18. Theapparatus of claim 16, wherein the data bit streams comprise a broadcastchannel bit stream comprising a transmission schedule, and wherein theprocessing resource is further configured to map the broadcast channelbit stream onto a fixed set of frequency sub-carriers centered about adirect current (DC) sub-carrier regardless of a system bandwidth. 19.The apparatus of claim 16, wherein the data bit streams comprise adownlink (DL) transmission control channel bit stream comprising amodulation coding scheme (MCS), and wherein the processing resource isfurther configured to map the DL transmission control channel bit streamonto a first set of frequency sub-carriers located near a higherfrequency edge of a system bandwidth and a second set of the frequencysub-carriers located near a lower frequency edge of the system bandwidthto provide frequency diversity.
 20. The apparatus of claim 16, whereinthe OFDM frame comprises a hybrid automatic repeat request (HARQ)indicator frame, wherein the radio front end interface is furtherconfigured to receive an uplink (UL) digital radio frame comprising a ULdata frame, wherein the processing resource is further configured togenerate the HARQ frame to provide a reception status associated withthe UL data frame, wherein the HARQ indicator frame comprises aplurality of frequency domain symbols, and wherein to perform thefrequency-time multiplexing, the processing resource is furtherconfigured to: map the frequency domain symbols onto a first set offrequency sub-carriers located near a higher frequency edge of a systembandwidth; and repeat the mapping of the frequency domain symbols onto asecond set of the frequency sub-carriers located near a lower frequencyedge of the system bandwidth to provide frequency diversity.
 21. Theapparatus of claim 16, wherein the data bit streams comprise a broadcastchannel data bit stream and a downlink (DL) control channel bit stream,and wherein the processing resource is further configured to perform anAlamouti type space-frequency block coding (SFBC) on the broadcastchannel bit stream and the DL control channel bit stream to providetransmit diversity.
 22. The apparatus of claim 16, wherein the digitalradio frame comprises a plurality of SC-FDMA symbols in time, andwherein the processing resource is further configured to map a non-timevarying pilot sequence (PS) onto all frequency sub-carriers in a systembandwidth in a SC-FDMA symbol time in the digital radio frame, andwherein the PS provides channel estimation capabilities in the systembandwidth.
 23. The apparatus of claim 16, wherein the data bit streamscomprise a downlink (DL) shared channel data bit stream associated withthe wireless backhaul remote unit, and wherein the processing resourceis further configured to: perform Reed Solomon (RS) encoding on the DLshared channel data bit stream to generate a plurality of RS codewords;perform byte interleaving across the RS codewords to generate aninterleaved frame; segment the interleaved frame into a pluralityinterleaved sub-frames; and perform Turbo encoding on each interleavedsub-frame to generate a Turbo codeword.
 24. The apparatus of claim 16,wherein the data bit streams comprise a broadcast channel data bitstream and a downlink (DL) control channel bit stream, and wherein theprocessing resource is further configured to perform tail-bitingconvolutional code on the broadcast channel bit stream and the DLcontrol channel bit stream.
 25. The apparatus of claim 24, wherein theprocessing resource is further configured to perform Reed Solomon (RS)encoding on the broadcast channel bit stream and the DL control channelbit stream prior to performing the tail-biting convolutional code. 26.The apparatus of claim 24, wherein the processing resource is furtherconfigured to perform rate matching and scrambling on the broadcastchannel bit stream and the DL control channel bit stream.
 27. Theapparatus of claim 16, wherein the processing resource is furtherconfigured to map a synchronization sequence (SS) onto a fixed set offrequency sub-carriers centered about a direct current (DC) sub-carrierregardless of a system bandwidth, and wherein the SS sequence comprisesa random Constant Amplitude Zero Auto-Correlation (CAZAC) sequence toprovide signal detection capabilities against a carrier frequencyoffset.
 28. The apparatus of claim 16, wherein the digital radio framecomprises a plurality of SC-FDMA symbols in time, and wherein theprocessing resource is further configured to perform a half sub-carrierfrequency shifting on the SC-FDMA symbols without a phase reset for eachSC-FDMA symbol.
 29. A wireless backhaul communication system,comprising: a transmitter comprising: a Reed Solomon (RS) encoderconfigured to perform RS encoding on a downlink (DL) data bit stream togenerate a plurality of RS codewords; a byte interleaver coupled to theRS encoder and configured to perform byte interleaving across theplurality of RS codewords; a Turbo encoder coupled to the byteinterleaver and configured to perform Turbo encoding on the interleavedRS codewords to generate one or more Turbo codewords, wherein each Turbocodeword is encoded from multiple RS codewords; a symbol mapper coupledto the Turbo encoder and configured to modulate and Discrete FourierTransform (DFT) precode the Turbo codewords, a transmission controlframe, and a broadcast frame separately, wherein the broadcast framecomprises a transmission schedule for a plurality of wireless backhaulremote units; and a sub-carrier mapper coupled to the symbol mapper andconfigured to generate a first digital radio frame comprising aplurality of symbols in time and a plurality of sub-carriers in a systembandwidth, wherein to generate the first digital radio frame, thesub-carrier mapper is to: map the DFT precoded broadcast frame onto afirst set of the sub-carriers centered about a direct current (DC)sub-carrier, wherein the first set of sub-carriers comprises a fixednumber of consecutive sub-carriers regardless of the system bandwidth;map the DFT precoded transmission control frame onto a second set of thesub-carriers near a lower frequency edge and near a higher frequencyedge of the system bandwidth; and map the DFT precoded Turbo codewordsonto frequency sub-carriers different than the first set of sub-carriersand the second set of sub-carriers; and a radio front end comprising anantenna and coupled to the transmitter, wherein the radio front end isconfigured to convert the first digital radio frame to a first analogsignal and transmit the first analog signal via the antenna.
 30. Thesystem of claim 29, wherein the transmitter further comprises a pilotsequence (PS) generator configured to generate a PS sequence and timemultiplex the PS sequence with the DFT precoded broadcast frame, the DFTprecoded transmission control frame, and the DFT precoded Turbocodewords, wherein the sub-carrier mapper is further configured to mapthe PS sequence onto all sub-carriers in the system bandwidth, andwherein the PS sequence provides channel estimation capabilities in thesystem bandwidth.
 31. The system of claim 29, wherein the transmitterfurther comprises a synchronization sequence (SS) generator configuredto generate a SS sequence and time multiplex the SS sequence with theDFT precoded broadcast frame, the DFT precoded transmission controlframe, and the DFT precoded Turbo codewords, wherein the sub-carriermapper is further configured to map the SS sequence onto a set ofsub-carriers spanning a same frequency band as the first set ofsub-carriers, and wherein the SS sequence comprises a random ConstantAmplitude Zero Auto-Correlation (CAZAC) sequence to provide signaldetection capabilities against a carrier frequency offset.